Some animal viruses may survive in imported feed ingredients

Researchers from South Dakota State University, Pipestone Veterinary Services in Minnesota and Kansas State University found that seven of the 11 animal viruses tested can potentially survive the transglobal journey from Asia or Europe to the United States in at least two commonly imported feed ingredients. The scientists examined virus survivability in 11 imported feed ingredients and products by replicating the environmental conditions in shipping containers.

“The findings of this study show that feed biosecurity should be a major priority for pork producers and ultimately, the livestock industry,” said assistant professor Diego Diel, who led the SDSU team. Scott Dee, director of research at Pipestone Veterinary Services, said, “For the first time, we have data to support that certain feed ingredients are risk factors for moving viruses between farms and around the world.”

Diel and his team at the South Dakota Animal Disease Research and Diagnostic Laboratory assessed the ability of 10 viruses to survive the 37-day journey from Beijing, China, to Des Moines, Iowa. One postdoctoral researcher, three research associates and a microbiologist worked on the project.

Kansas State University, which has a Level 3 biosecurity laboratory, evaluated the ability of African swine fever virus to survive the 30-day trip from Warsaw, Poland, to Des Moines. The Iowa destination was chosen because ingredients are mixed at a feed mill in Des Moines and then distributed to swine farms in the Midwest.

In previous work, Dee and ADRDL researchers discovered that porcine epidemic diarrhea virus (PEDV) can survive the simulated trip from Beijing to Des Moines in five feed ingredients—vitamin D, lysine, choline and organic and conventional soybean meal. That National Pork Board-funded research led to this larger study, which is supported by the Swine Health Information Center (SHIC). The study results are published in the March 20 issue of PLOS ONE.

Paul Sundberg, SHIC executive director, said, “This is foundational research. Dr. Diel and Dr. Dee identified a new avenue through which we may be transporting pathogens around the country and the world.” The researchers are now looking for cost-effective ways to mitigate this risk through continuing support from SHIC.

Identifying high-risk ingredients

Dee worked with a colleague at the Lincoln Memorial University College of Veterinary Sciences to expand the list of ingredients beyond those in the PEDV study. The researchers added soy cake and dried distillers grain solids (DDGS), moist and dry dog food and moist cat food. The use of feline calici virus and canine distemper as surrogate viruses further supported inclusion of these ingredients, he explained.

Because the U.S. also imports sausage casings, a product of pork origin, from Asia, the researchers added this product to the most recent study.

“We’re in a global economy; people and products are moving around the world,” Sundberg said. More than 47,000 tons of imported feed ingredients arrived in San Francisco from China in 2016, according to the International Trade Commission Harmonized Tariff Schedule.

Six viruses survived in conventional soybean meal, while only two did so in organic soybean meal. Though the researchers don’t know what accounts for this difference, Diel said preliminary analysis showed the organic soybean meal had a higher fat content and lower protein content.

Conventional soybean meal is treated with hexane, while the organic soybean meal was not, Dee explained. Because of the processing method used, the organic meal tested had a high fat content and lower protein level. “Those ingredients with higher protein levels seemed to be more conducive to virus survival,” he said.

Four viruses survived in soy oil cake, which is imported from China in the largest quantities of any of the ingredients evaluated. Only two viruses survived in DDGS, which ranks second among imported ingredients.

Four viruses survived in sausage casings. The amount of this processed product returning to the United States has quadrupled from 2012 to 2016.

Pinpointing key viruses

Due to the inability to work with certain target pathogens, surrogate viruses were used to study closely related and structurally similar viruses. For foot-and-mouth disease, Senecavirus A was studied. For classical swine fever, bovine virus diarrhea was reviewed. For pseudorabies virus, bovine herpes virus-1 was the surrogate. For nipah virus, canine distemper virus was substituted. For swine vesicular disease, research focused on porcine sapelovirus. And for vesicular exanthema virus, feline calicivirus was the surrogate.

“Certain ingredients seem to provide an ideal matrix for virus survival, and our study identified some of the high risk combinations of viruses and ingredients,” Diel explained. The SDSU team found viable Senecavirus A survived in all the ingredients except organic soybean meal. In addition, porcine sapelovirus survived in all ingredients except DDGS and choline.

African swine fever survived in eight ingredients. It was the only virus that survived the simulated trip without a feed matrix. Furthermore, when Iowa State researchers analyzed virus half-life, they found that African swine fever was most stable of the three viruses in conventional soybean meal.

The researchers also found that PRRSV can be added to PEDV as a pathogen circulating among swine in the United States that can survive the simulated trip from China and it did so in conventional soybean meal and DDGS. “That was really surprising because PRSSV is quite unstable,” Dee said.

“Though the original goal was to assess potential for transboundary movement, there are also implications for pathogen transport at the regional or national level,” Diel said.

“This research gives us a model to uncover potential pathways for pathogen transport,” Sundberg said. “Publishing the research in a peer-reviewed journal is extremely important. We want scientists to scrutinize it, repeat it and give constructive criticism. This underscores the importance and the credibility of the results and increases confidence in the outcomes.”

Dee said agencies, such as the U.S. Department of Agriculture and the Centers for Disease Control and Prevention, have shown interest.

“We all need to consider the implications of this research and then to understand if this potential transport could lead to transmission to animals and what we need to do next,” Sundberg said. “We must work together with government agencies and the feed industry to protect U.S. meat protein agriculture.”